After the now-famous star of Tabby, astronomers have discovered a double star with a strange luminosity in the Kepler satellite data. What could create the 28 drops of its brightness observed in 87 days?
A team of astronomers has discovered a new, strange star case with inexplicable variations in brightness. All their attempts to understand what may well cause the brightness decreases that have been detected by fire the satellite hunter of extrasolar planets Kepler, between August and November 2017, have been unsuccessful so far. Andrew Vanderburg of the University of Texas and his team have not found anything solid to elucidate the mystery of the 28 drops in brightness observed within 87 days on the EPIC star 249706694 (HD 139139). Located some 350 light-years from Earth in the direction of the constellation of the Serpent, the star is a little bigger and brighter than our Sun and evolves in couple with a red dwarf.
Initially, the researchers have of course thought of a procession of exoplanets passing in front of their star (planetary transit) but the periodicity of the falls of luminosity recorded is actually so random that they were baffled. Their occurrences “might as well be produced by a generator of random numbers,” they wrote in their study (available on arXiv). However, the indices weigh in favor of objects in transit which, passing in front of the light source, inflect the luminosity curves. But what is it? The researchers verified that the phenomenon is of an astrophysical nature.
What’s going on around the star HD 139139?
“Something weird is happening here,” said Hugh Osborn of the Marseille Laboratory of Astrophysics (LAM) at New Scientist magazine. It’s been ten years since we looked at the stars with this precision, but this is the first time we have found something that looks like a planet in transition but has no apparent periodicity.” And, indeed, for this to be a planet, they calculated that it would then be very difficult to explain what Kepler saw.
Another possibility remained: the transit of asteroids that eject dust. But it does not work, as the scientists found that they should all be surrounded by clouds of the same size. And if they were disintegrating planets, they should still have an unequivocal periodicity to their distant observers.
“All the transit scenarios we have mentioned seem to fail.” Like the famous KIC 8462852 alias Tabby’s star, the hypothesis of a megastructure of the Dyson sphere type enveloping this star has, of course, been invoked but the team recalls in passing that, often in astronomy, when we do not understand a problem, we bring in the extraterrestrials. We would like to believe that a civilization is behind the mystery of HD 139139, but the explanation of the vagaries of the brightness of this couple of stars is probably to look elsewhere, they argue.
Maybe it comes from inside one of the two stars itself? Astronomers have examined the hypothesis that these small changes in light could come from a stellar activity and disturbances like dark spots that stain the Sun. But again, it does not stick. The small drops in brightness are far from lasting a few days or weeks like sunspots.
In summary, for the moment, the mystery remains. We do not know what it is.